This invention relates to a color image pickup device using a solid-state device and especially to an improvement of a color filter device therefore.
Recently there has been considerable activity in developing color television cameras using solid-state image pickup devices. Among these, emphasis has been given to a single-plate type color television camera incorporating a single solid-state image pickup device, such as CCD, BBD, MOS devices or the like. In the case of single-plate type color TV cameras, experimentation has been directed to color filter arrays containing red, green and blue filter elements which are positioned adjacent the photosensors of the CCD. These elements are arranged in a finely checkered pattern, each one corresponding to a particular photosensor of the CCD. Examples of these prior art filter arrays are illustrated in FIGS. 1(A) and (B) which show the green filter elements (G) arranged in a checkered configuration and the remaining spaces being occupied by red (R) and blue (B) filter elements. In FIG. 1(A), R and B filter elements are not arranged along the same horizontal rows; while in FIG. 1(B), R and B filter elements are arranged along the same horizontal rows. Since interlaced scanning is normally used in television display systems, it is necessary to use a different arrangement of filter elements in adjacent pairs of rows, with the arrangement of filter elements within the rows of each pair being identical, as shown in FIGS. 1(A) and (B). For example, in FIGS. 1(A) and 1(B), the arrangement of filter elements within the rows of pair 1 are identical and the arrangement of elements within the rows of pair 2 are identical; however, the arrangement of filter elements in pair 1 are different than the arrangement of filter elements in adjacent pair 2.
As known in the prior art, the arrays shown in FIGS. 1(A) and 1(B) require the use of a 1H delay circuit (i.e., one horizontal line scan delay) to obtain a luminance signal (Y) corresponding to the brightness at each filter element. In FIG. 1(A), for example, by delaying the signals of the first line of pair 1 by 1H, coincidence is obtained with the scanning of the signals of the first line of pair 2. Thus, a green signal, from which the luminance signal is generated, is obtained for each filter element. The same luminance signal, however, is used for each pair of elements from which it was formed. For example, in FIG. 1(A), a luminance signal Y.sub.5-6 is formed from element 5 and is used for elements 5 and 6. However, if element 5 receives a dark image while element 6 receives a bright image, the resultant luminance signal will be dark. This resulting signal, while accurately representing the dark image of element 5 will not accurately represent the bright image of element 6. This results in deterioration of the vertical resolution.
FIG. 2 shows another example of a prior art color filter array which overcomes the disadvantages mentioned above. In this filter array, four different kinds of color filter elements, green (G), yellow (Ye), cyan (Cy) and white (W), are periodically arranged. Namely, Ye and Cy are alternately arranged along adjacent horizontal rows within element pairs 1,3 and all remaining odd element pairs. G and W are also alternately arranged along adjacent horizontal rows within element pairs 2, 4 and all remaining even element pairs. The cyan filter passes blue and green, while the yellow filter passes green and red. Since all of the filter elements pass the G light, there is no need to supplement the signals by utilizing a 1H delay for correcting vertical resolution.
This conventional solid-state image pickup device, however, has a problem in reproducing color images. This device fails to reproduce pure red and yellow colors; in fact, pale red and greenish yellow are reproduced, respectively, instead of pure red and yellow colors.
It has been found that this problem is caused by light leakage to neighboring picture elements. This leakage results in deterioration of pure color reproduction, as discussed above. This light leakage phenomena in solid-state devices is explained below in detail. In a CCD (Charge Coupled Device) image pickup device, for example, a plurality of spaced photosensitive areas or photosensors are provided which are registered with the filter elements of the color filter array. Each of the photosensors generates an electric charge, the amount of which is proportional to light intensity passing through the corresponding color filter element. This generated charge is transferred by potential wells successively formed in the device. Since the potential wells are usually formed in a surface area of the device, the field intensity within the potential wells is weaker than in the deep areas of the device. Since red light has a longer wavelength than green or blue light, red light is capable of entering into the deep areas of the device. When high intensity red light is incident on the photosensors, the excess charge generated in the deep area tends to enter the adjacent potential wells over the low potential barrier. Thus leakage is shown at 7 in FIG. 2.
In a solid-state image pickup device (i.e., an interline transfer device), any horizontal leakage of the excess charge is prevented by vertical transfer channels or overflow drains isolating the horizontally adjacent photosensors from each other. In any event, excess charges generated by high intensity red light leak to vertically adjacent potential wells, as shown by the vertical arrows in FIG. 2. High intensity red light incident through the Ye and W filter elements generates a large quantity of charges, and the excess charges vertically leak into adjacent green (G) and cyan (Cy) areas. This leakage, as discussed above, causes deterioration of the reproduced color image quality.